Gas separation processes using adsorbent beds are well known in the art. Typical adsorption based processes include those where at least one more adsorbable gas component is selectively adsorbed from a multi-component feed gas to produce a product gas containing one or more less adsorbable gas components. Of particular interest, but not limited thereto, are cyclic adsorption processes wherein at least one adsorbed gas component is removed from the adsorbent material using a reverse gas flow such as conducted in pressure swing adsorption (PSA) processes, vacuum swing adsorption (VSA) processes, vacuum pressure swing adsorption (VPSA) processes, or temperature swing (TSA) processes. These processes have evolved significantly over the last few years with improvements being made to the adsorbent materials, the adsorbent beds, and the overall process parameters and controls. Costs associated with the construction and operation of such plants are constantly being driven lower by competitive market pressures and it has become paramount to reduce the costs associated with designing, building, transporting and operating such plants by decreasing bed sizes and standardizing components. It is desirable to utilize smaller or compact bed structures for reducing the adsorbent material requirements; reducing the size of the plant equipment such as the process vessels and surge tanks; and also reducing the overall plant footprint including the transportation skid dimensions. Smaller skids in turn reduce transportation and installation costs.
The present adsorption bed structure brings together the benefits of a design utilizing; low inlet void volumes, large bed areas, and short bed depths (transfer lengths) in a modular and scalable adsorbent bed design requiring decreased adsorbent inventory and smaller plant equipment with smaller overall dimensions. These modular compact designs are more suitable for reduced transfer length geometry than conventional bed configurations since the larger vessels are hard to fabricate and have height and size limitations in such traditional configurations. This is particularly true for radial bed designs. Also, the capability of providing shorter cycle times now used with modern process intensification requirements are difficult to implement in the traditional larger configurations due to the high void losses and reduced valve life. For example, conventional radial or axial configurations would require several separate vessels which would make them uneconomical to construct and maintain.
It is therefore desirable to design new adsorbent bed systems for use in adsorption based gas separation processes that are generally smaller in size; require lower fabrication costs; are easier to transport; have less maintenance and repair requirements; and are easier to load with adsorbent material. It is equally important to design adsorbent beds that are smaller, but do not negatively affect the process flow; cycle speed; rate and volume of throughput; and potentially increase overall power requirements of the newer, more intensified processes. These smaller designs result in significant cost savings for an adsorption based gas separation plant.
Prior modular compact bed designs have been proposed. For example, U.S. Pat. Nos. 8,361,205 and 8,268,043 disclose two such designs. The present invention discloses a unique modular design which has advantages related to cost of manufacture and operation. In one aspect, the separate feed and product channels taught herein provide a more consistent flow distribution and less pressure drop resulting in a more balanced feed and product flow. Another aspect of the invention involves the fact that the assembly of the internal components makes the overall structure stronger and requires less overall materials of construction (normally carbon steel and often stainless steel) than previous designs. The external product manifold disclosed herein also enables the use of inexpensive welds or other techniques for sealing and makes it possible to use less expensive valves or other flow restricting devices or geometries to trim the gas flows into each modular compact adsorbent bed unit resulting in a more balanced process gas flow.